scsi: qla1280: set 64bit coherent mask

After Commit 54aed4dd

 ("MIPS: IP27: use dma_direct_ops") qla1280 driver
failed on SGI IP27 machines with

qla1280: QLA1040 found on PCI bus 0, dev 0
qla1280 0000:00:00.0: enabling device (0006 -> 0007)
qla1280: Failed to get request memory
qla1280: probe of 0000:00:00.0 failed with error -12

Reason is that SGI IP27 always generates 64bit DMA addresses and has no
fallback mode for 32bit DMA addresses implemented. QLA1280 supports 64bit
addressing for all DMA accesses so setting coherent mask to 64bit fixes the
issue.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>